Stabilizers and fixing agents for photographic silver halide emulsions



United States Patent Ofiice 3,242,232 Patented Apr. 19, 1966 3,247,232 STABILIZERS AND FIXING AGENTS FOR PHOTO- GRAPHIQ SELVER HALIDE EMULSIQNS George W. Luckey, Rochester, N.Y., assignor to Eastman Kodak Company, Rochester, N.Y., a corporation of New .lersey N0 Drawing. Filed Dec. 36 1960, Ser. No. 79,493

7 Claims. (Cl. 260-429) This invention relates to novel fixing agents and stabilizers for photographic silver halide emulsions and more particularly to metal salts of substituted arninomercaptans whose silver complexes are water-soluble, and compositions containing these compounds Developed photographic silver halide emulsion layers must be fixed and/ or stabilized by a chemical treatment in order to produce a permanent silver image. If the residual silver halide is left in the developed emulsion layer, it will be converted to silver upon exposure to light thus obliterating the image. To avoid this, the developed emulsion layer is fixed by using a fixing agent which forms a water-solube complex which is then washed out of the emulsion layer along with the fixing agent. Any residual prior art fixing agent and/or silver halide complex left in the emulsion layer are very detrimental to the image stability. When prior art fixing agents are left in emulsion layers, they form crystalline deposits upon drying and upon long standing tend to decompose and release sulfur or sulfur compounds which convert the silver image into silver sulfide. Similarly residual silver halide complexes formed with prior art fixing agents will tend to decompose upon standing with the formation of silver sulfide which reduces the image density and changes its color. An unfixed or an incompletely fixed silver image can be made more or less permanent by treatment with a stabilizing agent which forms a stable Water-soluble complex with the residual silver halide. These complexes may be left in the emulsion layer, however, it is desirable to remove most or all of them from the emulsion to produce an image of optimum permanence.

Fixing and stabilizing agents, such as the alkali or ammonium thiosulfates, ammonium thiocyanate, thiourea, thioglycolic acid, etc., are well known in the art. Compounds which stabilize an image may also be fixing agents, that is, they may convert the unexposed silver halide to a soluble salt which can be Washed from the emulsion. However, there are many stabilizers which are not good fixing agents and some fixing agents that are not good stabilizers.

A good stabilizing agent should have the following characteristics: (1) the silver complex formed should be relatively stable to sunlight, (2) the silver complex should be colorless, (3) the stabilizers should be odorless, nontoxic, non-deliquescent, (4-) the stabilizer that remains in the processed emulsion coating should not cause rapid bleaching of the silver image, and (5) the processed print should resist straining in an atmopshere of hydrogen sulfide. The two most essential properties are 1 and 2.

Among the known fixing and stabilizing agents are mercaptan compounds. These compounds have desirable fixing and stabilizing properties, however, these compounds along with almost all of the organic compounds used before have the disadvantage of liberating an equivalent amount of hydrogen ion for every equivalent amount of silver ion that is fixed or stabilized. This causes the fixing composition pH to change drastically during the fixing or stabilizing process thus decreasing the efficiency of chemical hardeners and causing deterioration of the gelatin or other harmful side reactions. For example, when a solution of 2-diethylaminoethanethiol hydrochloride is used to fix a medical X-ray film with a coarse grain silver bromoiodide emulsion such as Kodak Blue Brand Medical X-ray Film, the pH of the solution decreases from 4.5 to less than 2, and a yellow compound forms when the coating is dried without Washing. When Z-aminoethanethiol hydrochloride is used, a yellow sludge forms in the emulsion during the stabilization process and in the solution when the concentration of silver ion is sutficiently high and the pH is sufficiently low.

Many of the mercaptans which have been used as stabilizers react with the skin causing an odor which cannot be easily removed by washing. This is a serious disadvantage when the fixing and stabilizing baths are used in tray processing or in processes where they are likely to come in contact with personnel.

Prior art fixing agents when left in emulsion layers crystallize leaving very undersirable deposits which may make the images unusable. Solutions containing these agents when spilled result in crystalline deposits.

It is therefore an object of my invention to provide a novel class of improved fixing and stabilizing agents for developed photographic silver halide emulsions.

Another object is to provide as a novel class of fixing and stabilizing agents, metal salts of aminomercaptans which form water-soluble silver complexes and which are characterized by not liberating acid in the fixing bath during use.

Another object is to provide a novel class of stabilizers and fixing agents for developed photographic silver halide emulsions which are characterized by not forming a precipitate in the emulsion coating or in the areas where the solution is spilled.

Another object is to provide a novel class of stabilizers and fixing agents which are relatively rapid acting and Whose fixing rate is not changed by large dilutions with water.

Another object is to provide a novel fixing and stabilizing composition containing a metal salt of a substituted aminomercaptan which forms a water-soluble silver complex.

Another object is to provide a processing element which incorporates the novel stabilizing and fixing agents of my invention and which is used for fixing and stabilizing developed photographic silver halide emulsion layers.

' These and other objects of my invexntion are accomplished by using metal salts of substituted aminomercaptans which form water-soluble silver complexes. These salts have the formula:

RSMX

wherein R is a substituted aminoalkyl group in which the alkyl group has from 1 to 4 carbon atoms, such as methyl, ethyl, propyl, isopropyl, butyl, secondary butyl, tertiary butyl, etc.; M is a divalent heavy metal such as zinc, cadminum, lead, etc.; and X is an acid anion, such as chloride, acetate, lactate, sulfate, nitrate, etc. The substituents on the amino moiety of the aminoalkyl group may be a hydrogen atom, a lower alkyl group having from 1 to 3 carbon atoms such as methyl, ethyl, propyl, isopropyl, etc., such that no more than one of the substituents is a hydrogen atom, and these substituents may consist 2-diethylaminoethanethiol zinc acetate, Z-diethylaminoethanethiol cadmium acetate, Ethylaminoethanethiol zine acetate, 2-dimcthylaminoethanethiol zinc chloride,

' Di-isopr-opylaminoethanethiol zinc acetate,

Di-isopropylaminoethanethiol lead acetate, Di-n-propylaminoethanethiol zinc acetate, 2-morpholinoethanethiol zinc acetate,

'Z-morpholinoethanethiol cadmium acetate,

2-mercapto-3-morpholinopropanol zinc chloride.

These compounds are prepared by allowing the SH group of a mercaptan to react with a salt of a heavy metal other than silver. The RSMX compounds of my invention are prepared by heating equimolar mixtures of the mercaptan RSH and the heavy metal salt MX to a temperature of from 60 to 120 C. in water, alcohol, or

some other suitable solvent. This reaction liberates the acid of the anion in the metal salts. If this acid is volatile, a solution of the metal salt of the mercaptan in the solvent can be obtained. In some cases, the metal salt can be crystallized from the solution but in others the salt is very difficult to crystallize. The properties of these compounds depend upon the mercaptan and on the heavy metal salt. The cadmium salts, in general, are less soluble than the zinc salts and can be crystallized. The zinc acetate salt of 2-morpholinoethanethiol hydrochloride can be crystallized but the zinc acetate salt of 2-ethylaminoethanethiol hydrochloride cannot be crystallized. When an aqueous solution of the latter compound is evacuated for 24 hours the solvent evaporates leaving a colorless, glassy solid with no detectable crystal structure. This failure of the zinc salts to crystallize is a very useful property.

The compounds of my invention are characterized by properties which make them valuable for use in stabilizers and fixers for silver halide emulsions. For example, the zinc acetate of Z-diethylaminoethanethiol hydrochloride is a colorless, glassy solid without detectable crystal structure. Gelatino-silver halide emulsions that contain this salt have been stored for 3 months without any observable crystallization and solutions of this salt do not form objectionable crystalline deposits when they are spilled.

All of my compounds are characterized by not liberating hydrogen ions when they are used to fix or stabilize silver halide emulsions. This means that the efiiciency of stabilizing hardeners used in the fixing and stabilizing compositions is not decreased as they are when prior art stabilizing agents are used. Since there is no release of hydrogen ions, the deterioration of gelatin and other harmful side reactions do not occur when my stabilizing a gents are used. This very valuable property also makes it unnecessary to incorporate bufiering chemicals in the fixing and stabilizing compositions containing my compounds. This makes my compositions simpler than prior art compositions. As a result, photographic elements fixed and stabilized by my compositions are easier to wash than those treated with prior artcompositions.

Although my metal salts of aminomercaptans are usually used as the sole fixing and stabilizing agent in such a composition, it is possible to obtain desirable results by blending several of these zinc salts. For example, the zinc salt of 2-aminoethanethiol hydrochloride is a very rapid fixing agent but forms an insoluble precipitate when the silver ion concentration reaches a certain level, while the zinc salt of the diethyl compound does not form a precipitate as rapidly but also does not fix as rapidly. Consequently, equal volumes of the zinc salts of Z-aminoethanethiol hydrochloride and 2-diethylaminoethanethiol hydrochloride have been blended and used as a concentr-ated fixing bath. When one part of the bath is diluted by 8 parts of water by volume, coarse grain silver bromoiodide emulsion type medical X-ray films such as Kodak Blue Brand X-ray Film and Kodak No-Screen Medical X-ray Film can be fixed with a blended solution and washed more rapidly than when a rapid fixer with hardener is used that has the formula:

FORMULA A Solution A:

Ammonium thiosulfate g 150 Sodium sulfite (desiccated) g 12 Glacial acetic acid cc 9 Boric acid g 7.5 Water to cc 250 Solution B:

Aluminum chloride hexahydrate g 12.5 Water to cc 25 Combine solutions A and B and dilute with water to one liter.

The blend of the two zinc salts has the fading properties of Z-aminoethanethiol hydrochloride salt. When the proportion of diethylaminoethanethiol in the mixture is increased, the rate of clearing decreases but the fading properties are still similar to those of the 2-aminoethanethiol. When the silver ion concentration in the 50:50 bath increases, some precipitation occurs in the emulsion layers. This is easily removed by washing in water.

Greater dilutions of my fixing and stabilizing solutions can be used than is possible with prior art compositions without a proportional sacrifice in fixing rate. For example, a silver bromoiodide emulsion type medical X-ray film such as Kodak Blue Brand X-ray Film is fixed in 40 seconds at 25 C. with a 50:50 concentrate that is diluted with 4 parts of water, in 50 seconds when the solution is diluted with 10 parts of water, in 70 seconds when diluted 15 fold, and seconds when diluted 20 fold.

The metal salts of substituted aminomercaptans of my invention apparently do not react with the skin in the same way that the aminomercaptans per se do, or if they do, the rate and extent of the reaction are negligible. After immersion in the solutions, the skin can be cleaned by a simple wash in soap and water and no persistent odor remains. It appears that in the preparation of these metal salts, odor producing impurities are removed from the solution perhaps as insoluble salts of the more volatile mercaptans.

My compounds are characterized by having very low dissociation in water solution. For example, the zinc acetate salt of Z-aminoethanethiol hydrochloride has an equilibrium dissociation of about 10 Because of the very low dissociation of these compounds, the discovery that the formation of the metal salt complex such as the zinc or the cadmium complex has relatively little effect on the rate of fixation was unexpected. Apparently the rate of dissociation of the complex is very rapid when compared with the rate of fixation.

' Concentrated hardening fixing baths have been prepared by mixing the zinc salt of diethylaminoethanethiol' hydrochloride with glutaraldehyde or 'succinaldehyde. This is a unique property of metal salts; if the mercaptoamine is mixed with the glutaraldehyde or succinaldehyde, mercaptals form and the fixing and hardening rates decrease. Hardening fixing baths containing mercaptals of glutaraldehyde and succinaldehyde release acid during' the fixing process which reduces their stability. When the zinc salts are used, there is no decrease in either fixing or hardening action even when the salts are stored for 3 months at room temperatures. The hardening action of these aldehyde zinc salt baths is actually superior to that of the normal aluminum hardening fixing baths of the prior art and again there is no danger of forming a precipitate in the emulsion coating or in areas where the solution is spilled. These solutions are buffered in the acid region (pH of 3.5 to 4.5) so that the hardening action of the glutaraldehyde is not impaired by the release of acid.

Where a controlled release of acid during the fixing process is desired, this can be achieved by adding the appropriate amount of free mercaptan to the fixing bath. Solutions that are made from a compound that is made from /2 mole of zinc acetate and 1 mole of diethylaminoethanethiol hydrochloride have this property.

Hardening fixing baths have also been made by adding aluminum compounds to metal salt fixing baths. However, these do precipitate in emulsions when they are not washed out and the concentration that can be achieved is not nearly as good as that of the glutaraldehyde baths.

The compounds of my invention can be used in mono baths, solvent transfer, and in other applications where sodium thiosulfate or analogous silver halide solvents are now used.

The preferred metal salts of substituted aminomercaptans of my invention have at least one alkyl substituent on the amino group. Thus the zinc acetate salt of di ethylaminoethanethiol hydrochloride yields a more stable image than the corresponding aminoethanethiol salt. In general, it has been observed that as the number of carbon atoms in the alkyl substituents on the amino group of my compound is increased, the activity of the compound decreases.

The following examples will further illustrate the preparation of specific fixing and stabilizing agents of my invention, and will illustrate the valuable properties shown by compositions containing them. These compositions include solutions in which developed silver halide emulsion layers are fixed and/or stabilized, and also processing elements or webs incorporating the compounds of my invention which are squeegeed against the developed silver halide emulsion layer and then stripped off after the silver image has been fixed and/ or stabilized.

Example 1 Sixty-eight grams of diethylaminoethanethiol hydrochloride were dissolved in 18 grams of water and heated to 60 C. Eighty-four grams of zinc acetate dihydrate were added to the warm solution, and the mixture heated with stirring to 110 C. The volume of the solution after filtration was 120 ml. and the total weight was 156 grams. When one part of this solution was diluted with 9 parts of water by volume, the resulting solution had a pH of 4.4. When the solution was diluted with three parts of water, it cleared a 50 micron thick coating of nuclear track emulsion in 16 minutes at 23 C. The coating was dried without washing and stored for three months at room temperature. During this tnne, no crystallization or yellowing of the thick coating occurred.

A similar emulsion that was stabilized with an ammonium hypo fixer consisting of Solution A of Formula A diluted to one liter was filled with crystals after drying. Another 50 micron emulsion, stabilized with the solution of the formula:

FORMULA B 2-diethylaminoethanethiol-HCl g 533 Water to l 1 diluted with ten parts of water, was sticky and formed a saturated yellow color after prolonged storage.

When some of the zinc salt solution was placed on the hands, it was removed without any odor remaining; the solution of Formula B caused odor when handled in a similar way.

Example 2 A stabilizing bath was prepared by mixing equimolar quantities of zinc acetate and diethylaminoethanethiol as in Example 1. The concentrated solution was diluted with 4 volumes of water and enough glutaraldehyde was added to yield a concentration of 25 grams per liter. This solution cleared wet low contrast, coarse grain silver 6 bromoiodide emulsion film such as Kodak Matrix Film in 60 seconds at 23 C. and the processed emulsion did not soften or reticulate when immersed in water at 45 C. Wet Kodak Blue Brand Medical X-ray Film cleared in seconds at 23 C. The pH of the dilute solution was 4.5, and this did'not change when 160 8 x 10 inch sheets of the unexposed X-ray film were processed in one gallon of the solution. The hardening properties were unaffected by this exhaustion, but the clearing time in creased from 90 seconds to seconds. The properties of this solution were unchanged after storage for 3 months at room temperature.

A fixing bath with the following formula:

FORMULA C Sodium thiosulfate g 240 Sodium sulfite (desiccated) g 15 Acetic acid, 28 percent cc 48 Boric acid, crystals g 7.5 Potassium alum g 15 Water to l I cleared the X-ray film in about 45 seconds under these conditions, but it should be remembered that additional fixing time and washing were needed to prevent crystallization in the processed film. The pH of this solution did not change during exhaustion with 160 8 X 10 inch sheets of the X-ray film, but the clearing time increased from 45 seconds to 90 seconds.

A fixer with hardener bath having Formula A cleared the X-ray film in about 2() seconds under these conditions, but again, additional fixing time and washing were needed to prevent crystallization. The clearing time increased to about 30 seconds when 160 8 x 10 inch sheets of fiim were processed in one gallon of the solution. Thus, the over-all time for processing X-ray film was comparable with that of the zinc salt bath.

The fading of silver images was tested with a paper support coated with a silver chlorobromide printout emulsion such as Kodak Linagraph Direct Print Paper. Since printout images are composed of very finely divided silver, they are particularly susceptible to fading. Samples of exposed print paper were bathed in a solution having the Formula A with and without 10 grams of silver nitrate per liter and in the zinc salt bath. The printout images that were processed in the hypo bath faded within 10 minutes when no silver ion was present in the solution. If silver ion was present, the images faded somewhat and the background areas became brown. The images also had a warm tone. The image that was fixed in the zinc salt bath did not fade appreciably and the background areas had a cream color, even after storage for two and one-half months at room temperautrc.

Example 3 The zinc acetate and cadmium acetate salts of 2-diethylaminoethanethiol and 2-morpholinoethanethiol hydrochlorides were prepared by heating equal molar quantities in aqueous solution as described in Example 1. The Zinc salt of the morpholino compound formed a clear colorless solution, the cadmium salt had a pale yellow color. These solutions were diluted to five times their volume with water and used to stabilize Kodak Linagraph Direct Print Paper. The images stabilized in this way were stable for one week at 50 C. and 100 percent RH. while a similar image stabilized with a fixing bath with Formula C faded completely.

The solutions of the zinc salts of diethylaminoethanethiol and Inorphoiinoethanethiol hydrochlorides cleared wet medical X-ray film in 70 seconds. The cadmium salt solution of the diethylamino compound required seconds and the cadmium salt of the morpholino compound required more than this. The latter solution yielded a white sludge caused by the liberation of bromide ion during the fixing process. The cadmium salts were much more sensitive to bromide ion than the zinc salts; both were precipitated by iodide ion, when its concentration was 100 grams per liter. This precipitation reaction was specific; potassium sulfate and potassium chloride did not cause precipitation when added in concentrations similar to those of the potassium bromide and potassium iodide, but potassium thiocyanate did.

The solution of the zinc salt of 2-morpholinoethanethiol hydrochloride crystallized when it was dried, and gelatin coatings made from a water solution that contained 30 percent morpholinoethanethiol zinc acetate and 7 percent gelatin, also crystallized when dried. The zinc chloride salt of morpholinoethanethiol cleared wet medical X-ray film in 70 seconds at 25 C. when its concentration was between 100 and 400 grams per liter. This salt was a white crystalline compound, readily soluble in water. The solution that contained 100 grams per liter had a pH of 4.1.

Example 4 The zinc acetate salt of Z-aminoethanethiol hydrochloride was prepared by heating 90.8 grams of the thiol with 87.8 grams of zinc acetate dihydrate in 50 ml. of ethanol, to a temperature of 115 C. The final weight of the solution after heating was 164 grams. This concentrate was diluted so that the dilute solution contained the equivalent of 226 grams per liter of mercaptan. This dilute solution cleared wet Kodak Blue Brand Medical X-ray Film in 20 seconds and wet Kodak No-Screen X-ray Film in 150 seconds at 26 C. When the temperature was increased to 50 C., a solution of the zinc salt equivalent to 175 grams of mercaptan per liter cleared Kodak No- Screen X-ray Film in 90 seconds. However, the solution did not tolerate appreciable amounts of silver ion; subsequent samples of film had a white turbidity and a similar White precipitate ultimately formed in the solution. This precipitate seemed to be a compound of zinc, silver, and 2-aminoethanethiol; it did not form in solutions of the zinc salt of diethylaminoethanethiol, or in solutions that contained more than 50 percent of the diethyl salt. In the latter case, the precipitate that formed in the emulsion washed out with water.

Example 5 The zinc acetate salts of 2-aminoethanethiol hydrochloride and 2-diethylaminoethanethiol hydrochloride were prepared as described in Examples 1 and 4. The concentrated solutions were then mixed to form blends that contained 0, 25, 50, 75, and 100 percent of the zinc acetate salt of the diethylaminoethanethiol hydrochloride (Zindeaet) by volume. One part of each blend was diluted with four parts of water to form working solutions which were used to fix Kodak No-Screen Medical X-ray Film. The tunes to clear this film are summarized in the table below:

Time to Solution Composition Clear in Remarks Minutes 100% Ziudeaet. 8 No sludge observed.

75% Zindeaet 6 Do.

50% Zindeaet. 4. 5 Do.

25% Zindeaet 3 D0.

0% Zindeaet 3 Sludge in solution and in film.

100% Zindeaet, 80 g./l. AgNO; 29 Sludge in dry film,

was removed by wash.

75% Zindeaet, 80 g./l. AQNOs 14 Sludge in wet film,

was removed by wash.

50% Zindeaet, 8O g./l. AgNOa 7 Do.

25% Zindeaet, 80 g./l. AgNOa 6 Sludge in wet film and solution.

0% Zincieaet, 80 g./l. AgNOi 6 Do.

Print out images on Kodak Linagraph Direct Print Paper faded within 18 hours at 70 C. and 100 percent R.H. when they were stabilized with solutions that contained the zinc acetate salt of 2-aminoethanethiol hydrochloride. The images that were stabilized with the salt Example 6 Equal volumes of the zinc acetate salts of 2-aminoethanethiol hydrochloride and 2-diethylaminoethanethiol hydrochloride were mixed. One volume of this mixture was dilute-d with four volumes of water to form the working solutions. A working solution that contained 16 grams of silver nitrate per liter, and had a pH of 2.5, cleared wet Kodak Blue Brand Medical X-ray Film in 105 seconds. However, this was not a true clearing time. The film actually fixed in about 35 seconds, and the remaining time was required for the precipitated silver zinc aminoethanethiol complex to dissolve and diffuse out of the film. A wet X-ray film, placed in the fixing solution for 35 seconds, then washed for 30 seconds, cleared completely. A similar film fixed in a rapid fixer with hardener of Formula A for 35 to 40 seconds and bathed for an additional minute in water to remove the hypo, was not nearly as clear as the film that received the 65 second process in the blended fixer.

Example 7 A stabilizing bath was prepared by mixing 2.115 grams of ethylaminoethanethiol hydrochloride with 10 m1. of water at 50 C. Then 3.29 grams of zinc acetate dihydrate were added and the solution heated to 60 C. The volume of the solution was increased to 25 ml. and evacuated with a Water pump for 10 minutes. The solution was cooled and the pH adjusted to 3.5. This bath cleared wet Kodak Blue Brand Medical X-ray Film in 55 seconds at 25 C., and cleared an industrial X-ray film with a coarse grain silver bromoiodide emulsion such as Kodak No-Screen Industrial X-ray Film in 5 minutes and 30 seconds at the same temperature.

Example 8 A stabilizing bath was prepared by mixing 4.45 grams of 2-mercapto-3-morpholinopropanol, 3.43 grams of zinc chloride and 25 ml. of methanol. The mixture was heated until the zinc chloride dissolved, then water was added to increase the volume to 25 ml. This stock solution was mixed with additional water to make a solution which contained 0.6 mole of sulfur per liter. At a pH of 4.0, the 0.6 m. solution cleared Kodak Blue Brand Medical X-ray Film in seconds at 25 C.

Example 9 A stabilizing bath was prepared by mixing 4.25 grams of Z-dimethylaminoethanethiol hydrochloride with 4.09 grams of zinc chloride and 85 grams of water. Sodium carbonate was added to maintain the pH between 5 and 6 while heating the mixture to 70 C. After cooling to 20 C., the pH was decreased to 3.5 with hydrochloric acid. At 20 C., this solution cleared 'wet Kodak Blue Brand Medical X-ray Film in 150 seconds.

Example 10 A stabilizing bath was prepared by mixing 2.96 grams of di-isopropylaminoethanethiol hydrochloride with 3.25 grams of zinc acetate dihydrate and 15 ml. of water. This mixture was heated to C. and kept at this temperature for 10 minutes followed by exacuation with a water pump for 30 minutes as the solution cooled. The volume was then increased to 25 ml. with water and the pH was adjusted to 3.5 with hydrochloric acid. This solution cleared wet Kodak Blue Brand Medical X-ray Film in seconds at 25 C.

Example 11 A stabilizing bath was prepared by mixing 18.9 grams of lead acetate, 8.5 grams of diethylaminoethanethiol 9 hydrochloride and 5 grams of water. The mixture was heated to 70 C. until the lead acetate dissolved. The viscous liquid was then diluted to 100ml. with water. The pH of this diluted solution Was 4.2. At a temperature of 75 F., this solution cleared Kodak Blue Brand Medical X-ray Film in 120 seconds.

Example 12 A stabilizing bath was prepared by mixing 2.96 grams of di-n-propylaminoethanethiol hydrochloride with 3.29 grams of zinc acetate dihydrate and 15 ml. of water. This mixture was heated to 105 C. and kept at this temperature for minutes followed by evacuation with a water pump for 30 minutes as the solution cooled. The volume was then increased to 25 ml. with Water and the pH was adiusted to 3.5 with hydrochloric acid. This solution cleared Wet Kodak Blue Brand Medical X-ray Film in 320 seconds at 25 C.

Similarly, other metal salts of aminomercaptans are used in baths for fixing and stabilizing silver images in freshly developed silver halide emulsion layers.

The following examples will illustrate how my compounds can be incorporated in hydrophilic layers such as gelatin then stored for use at a later time to fix and/or stabilize silver images in freshly developed silver halide emulsion layers.

Example 13 The extreme compatibility of the zinc salt fixing bath with gelatin was studied by making gelatin coatings. Seven grams of bone gelatin was dissolved in 100- ml. of an aqueous solution that contained 30 grams of zinc acetate salt of diethylaminoethanethiol hydrochloride. The zinc salt was prepared by dissolving equal molar amounts of diethylaminoethanethiol hydrochloride and zinc acetate in isopropanol and heating. A small amount of water was added to accelerate the reaction. After drying, the zinc acetate salt was added to water to make the solution.

The gelatin solution of the zinc salt was coated at a wet thickness of 0.003 inch on 0.003 inch thick acetate butyrate support and also coated on 0.0015 inch support. The coatings dried without crystallization and no curl was observed even after storage for one month. Thus, large amounts of the zinc salt can be retained by a gelatin coating without damage to its physical properties. These fixing sheet coatings contain more than enough fixing agents to clear one side of Kodak Blue Brand Medical X-ray Film.

Example 14 A processing element for stabilizing a silver image was prepared by coating a transparent support with a 0.003 inch thick coating of a coating melt having the composition:

G. Diethylaminoethanethiol zinc acetate 6.0 Gelatin 5.0 Water to 100.0

An exposed silver halide emulsion layer was developed in a conventional photographic developer and immediately laminated to a sample of the above-described stabilizing sheet. Room lights were turned on in 15 seconds with no visible effect on the image in the photographic emulsion. Extended keeping of this stabilized image showed no further action of light on the photographic emulsion and no developer stain.

Another sample of the developed silver halide emulsion layer Was stabilized by bringing a hardened gel stabilizing pad into contact with it for a short time and then re moving the pad leaving the processed emulsion layer with a silver image that was stable to roomlight exposure and free of developer stain.

Similarly, other metal salts of my aminomercaptans can be incorporated in layers of a hydrophilic material such as gelatin, polyvinyl alcohol, polyvinyl butal, polyvinyl acetate, ethyl cellulose, methyl cellulose, copolymers of acrylic acid and acrylonitrile, such as are disclosed in Calvier et al., US. Serial No. 541,547, filed October 19, 1955, now US. Patent 2,968,558, issued January 17, 1961 etc., to make fixing and stabilizing pads or webs according to my invention. Some zinc salts of my invention are particularly well suited for incorporation in pads or webs used for fixing and/or stabilizing photographic images since these salts do not crystallize. Usually these layers are coated on a suitable support to facilitate handling the element. The support for a stabilizing pad that is to be laminated to a developed photographic element may be a thin layer of any material that is transparent, colorless, permeable to water but preferably not permeable to the metal salts of my invention. The supports used for fixing and stabilizing pads or webs that are held in contact with the developed photographic layer for the fixing and stabilizing step and then separated from the completely processed layer may be any of those that are satisfactory for the lamination type of pad, however, this support can be opaque and need not be water-permeable.

The .aminomercaptan hydrochlorides used in making my metal salts may be made in a manner similar to that used by Gabriel, Ber. 22, 1137 (1889) abstracted by Chem. Abstracts 31, 1362 if they are not readily available commercially.

The preferred metal salts of substituted aminomercaptans form water-soluble silver complexes, however, it is possible to make such salts that will form water-insoluble silver complexes.

The novel metal salts of aminomercaptans of my invention are valuable agents for fixing and/ or stabilizing the silver image in a developed silver halide emulsion layer. They are characterized by being relatively rapid acting fixing and stabilizing agents. They have the valuable advantage over prior art organic fixing and stabilizing agents of not releasing an equivalent amount of hydrogen ions for every equivalent amount of silver ion fixed as do the prior art agents. Thus my fixing and/ or stabilizing compositions do not loose their effectiveness because of a decrease in pH during use as do prior art compositions. Because of this, my compositions may be used to treat larger amounts of a given kind of film than is possible with prior art compositions before becoming exhausted. My agents are characterized by not forming mercaptals with the hardening agents glutaraldehyde and succinaldehyde when used with them in a hardening fixing bath. Prior art agents such as the aminomercaptans when used in such hardening fixing baths form mercaptals which become ineffective as hardening agents when sufiicient acid has been released by fixation so that the hardening reaction is inhibited. Compositions containing my metal salts of aminomercaptans may be readily washed from the users hands without leaving the strong, unpleasant odor characteristic of prior art mercaptans. Some of my compositions do not crystallize upon drying and therefore photographic elements treated with them can be dried without washing and yet be free of crystalline deposits. Some of my zinc salts are particularly valuable for incorporating in the hydrophilic layers of fixing and/or stabilizing pads that are superior to prior art pads. Since the silver complexes of my salts are transparent and colorless when left in emulsion coatings, the stabilizing pad can be laminated to the developed photographic emulsion layer.

The invention has been described in detail with particular reference to preferred embodiments thereof but it will be understood that variations and modifications can be effected Within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

I claim:

1. A compound having the formula:

RSMX

wherein R represents an N-substituted aminoalkyl group selected from the class consisting of an N-alkyl'amino- ,alkyl group, a N,N-dialkyl'aminoalky1 group and an N- morpholinoalkyl group, in which the alkyl'moiety has from 1 to 4 carbon atoms and the alkylmoiety has from 1 to 3 carbon atoms; M is a metal selected from the class consisting of zinc, cadmium and lead; and X is an acid anion.

2. A compound of claim 1 in which M represents ZlIlC.

3. The compound 2-dimethylaminoethanethiol zinc chloride.

4. The compound ethylaminoethanethiol zinc acetate.

5. The compound 2-diethylaminoethanethiol cadmium acetate.

6. The compound di-isopropylaminoethanethiol zinc acetate.

12 7. The compound 2-diethylaminoethanethiol zinc acetate.

References Cited by the Examiner UNITED STATES PATENTS TOBLAS E. LEVOW, Primary Examiner.

HAROLD BURSTEN, ABRAHAM H. WINKELSTEIN,

Examiners. 

1. A COMPOUND HAVING THE FORMULA: 